Self-releasing bushing of the type employing wedge rings with solid antifriction coatings thereon have been employed with commercial success to transmit thrust and torque between a hub and shaft without the use of conventional keys. Representative bushings of this type are disclosed in U.S. Pat. Nos. 3,501,183 and 3,638,974; both issued to Andrew Stratienko. The coated mating inclined surfaces of these bushings have a relatively low angle of inclination, on the order of 3.degree.. This shallow wedge angle, in conjunction with the low-friction contact provided by the antifriction coating offers very little resistance to axial sliding movement between the inner and outer wedge rings. In fact the shallow wedge angle, low friction construction makes the wedge rings of the bushing both self-tightening and self-releasing, as is more fully explained in the '183 patent. In addition, only a low tightening force is required to obtain an extremely powerful grip between axially straight surfaces of the bushing and the machine element or part to be interconnected by said bushing. However, due to the fact that the engaged inclined surfaces of the inner and outer wedge rings are very slippery it is very desirable to employ a wedge ring rotational stop to engage the inner and outer wedge rings for preventing relative rotational motion between them under high load conditions. This introduces an additional element into the bushing construction, and also requires close manufacturing tolerances to permit positive torque transmission, particularly for preventing backlash when the elements that are interconnected by the bushing are intended to transmit cyclic, reverse loads.
To eliminate the need for using a rotational stop between inner and outer wedge rings of a keyless bushing it has been suggested to do away with the low friction coating on the engaging inclined surfaces of the wedge rings. One such bushing is sold under the trademark "TranTorque" by Manheim Manufacturing and Belting Co. of Manheim, Pa. In the TranTorque device the outer wedge ring is interconnected through a rib and groove arrangement with a single, concentric, annular nut having an internal threaded surface in threaded engagement with the outer periphery of an axially straight segment of an inner wedge ring. The annular nut has flats provided on its outer periphery that are adapted to be engaged with a torque wrench. Rotation of the nut in one direction will move the inner and outer wedge rings along their mating inclined surfaces for expanding the outer wedge ring and contracting the inner wedge ring to establish a thrust transmitting connection between a machine component or part and a shaft. Rotation of the nut in the opposite direction will release this connection.
Establishing torque capacity through the use of a single annular nut that has an internal threaded diameter larger than that of the shaft over which it is positioned imposes severe limitations on the use of the TranTorque bushing. Specifically, the wrench torque necessary to establish the desired axial force between the wedge rings is directly proportional to the diameter of the threaded surface through which the force is induced (i.e. the larger the diameter the larger the required wrench torque), and is inversely proportional to the number of threaded members (i.e. nuts, screws) through which the axial force can be divided (i.e. the smaller the number, the larger the required wrench torque).
The use of the single threaded nut to transmit axial force in the TranTorque bushing establishes wrench torque requirements that make it impractical, or undesirable for use on shafts having a diameter in excess of about 11/4 inches. Therefore, useage of the TranTorque bushing is relegated to relatively small systems.
Another keyless torque transmitting bushing employing wedge members that do not need to be interconnected by a rotational stop is manufactured by Dyna-Lok Inc. of Ringwood, N.J. This bushing includes inner and outer wedge members having mating tapered surfaces that are free of a low friction coating. To permit the bushing to be assembled the outer wedge member is made in the form of two separate rings segments, each of which is independently tightened by loading screws threadedly engaged within openings of a flange integrally formed as part of the inner wedge member. In view of the fact that the outer wedge member is formed of independently activated, discrete segments, the bushing is not a self-centering device, and will not provide a concentric connection between a shaft and hub. The necessity of forming the outer member of separate segments results from the fact that the inner member is provided with an integral flange adjacent the thin end, or low side of its inclined outer surface. Therefore a unitary outer member having a mating inclined inner surface cannot be positioned over the inner member from the side opposite the flange. Thus the necessity of forming the outer member in discrete segments.
Although the Dyna-Lok bushing does not include multiple loading screws for tightening it to firmly interlock a shaft to a hub member; it is not designed or constructed to include any releasing mechanism. Due to the fact that there is no releasing mechanism it often is necessary to remove the bushing by hammering, or otherwise pounding on it. This is a difficult operation, is impractical in large systems, and can damage the bushing.
In summary, although the Dyna-Lok bushing is capable of transmitting torque between a machine component and a shaft without employing a rotational stop between the inner and outer wedge members; it is neither self-centering nor self-releasing. Moreover, it does not include any arrangement to facilitate releasability.
Quick detachable bushings (referred to in the trade as QD-type bushings) are commonly employed with conventional keys to permit the mounting of the same sheave, sprocket, pulley or other machine element to slotted shafts of different diameters, or to permit the mounting of machine elements having different hub dimensions to the same slotted shaft. These QD-bushings include only a single split ring having an inclined outer surface for engaging an inclined inner surface defining an opening through the hub of the machine element. The inner surface of the ring is axially straight for receiving a shaft therethrough, and for tightening on the shaft when installed within the opening through the hub. In addition, the inner surface of the ring is provided with a keyway for receiving a corresponding key associated with the shaft. A flange is formed integrally with the bushing at one end thereof, and this flange is provided with a plurality of circumferentially spaced passages, some of which are adapted to be oriented in axial alignment with circumferentially spaced passages formed directly in the sheave, sprocket or other machine element. Cap screws cooperate with the axially aligned passages of the flange and machine element to tighten the bushing within the tapered opening in the hub. When the cap screws initially are directed through the machine element, and then into the bushing flange (standard mounting), the passages in the bushing flange are threaded to permit the cap screws to provide their tightening function. When the cap screws initially are directed through the bushing flange, and then into the sheave or pulley (reverse mounting), the passages in the sheave or pulley are threaded to permit the tightening action to be achieved.
In the standard mounting arrangement threaded passages also are formed in the machine element. These latter passages are in axial alignment with solid surfaces of the bushing flange to permit cap screws to thread into the machine element, and thereafter push the bushing out of the tapered opening through the hub when detachment of the bushing is desired. Obviously the cap screws employed to secure the bushing to the machine element must be removed in order to permit this separation to take place.
In the reverse mounting arrangement threaded passages through the bushing flange axially align with solid surfaces of the machine element to permit the use of cap screws to separate the bushing from the tapered opening through the hub. The manner in which this is accomplished is substantially the same as for releasing the standard mounting arrangement, and is not believed to require any further explanation.
In many sheaves, sprockets and other machine elements the hub section including the inclined inner surface is either located closer to one axial end than the other, or is otherwise unsymmetrical with respect to a central vertical plane through such machine elements. In some systems the desired position of these machine elements will dictate the axial orientation of the machine element on the shaft. This also will fix the orientation of the QD bushing relative to the components of the system because the bushing can only be inserted into the hub from one direction; dictated by the direction of inclination of the inner hub surface. The particular mounting arrangement that needs to be used (i.e. standard or reverse) is dictated by the position of the bushing elements relative to the other components of the system. Therefore, provision for both types of mountings should be made in the construction of the machine element by providing the necessary arrangement of threaded and unthreaded openings in the hub section to cooperate with appropriate openings in the flange of the QD bushing. This complicates the manufacturing of the machine element, and can also significantly weaken the hub section. Particularly, as compared to a machine element in which the hub section does not need to be provided with any such openings.
It is important that the taper of the inner hub surface of the machine element matches the outer inclined surface of the QD bushing, and also that the mounting openings in the bushing flange match with proper mounting openings in the hub. However, since the QD bushings are manufactured by a different source than the sheaves or pulleys, the manufacturing tooling needs to be matched by different entities. This is undesirable and can create tolerance problems.
Although the single ring QD type bushings are significantly different in construction and mode of operation from the dual wedge ring bushings forming the subject matter of the instant application, they have been referenced herein because the mechanism by which they are assembled with, and detached from a sheave or pulley might be regarded as similar to the mechanism employed in the instant invention. However, it is important to recognize that QD-type bushings include only a single tapered ring, and therefore do not teach any structural cooperation of elements for dual wedge ring constructions of the type constituting the instant invention, let alone the unique cooperation of the structural elements invented by applicant. Another extremely important point is that the sheaves or pulleys to which the QD-type bushings are secured are machine elements; not the equivalent of an expandable and contractible outer wedge ring of the type employed in the dual wedge ring bushings of this invention. In fact many of the skills, techniques and considerations employed in the manufacture of sheaves, pulleys and similar machine components are totally unrelated to the skills, techniques and considerations employed in the manufacture of dual ring power transmission bushings of the type forming the subject matter of the instant invention, and are actually manufactured by different sources.